1. Field of the Invention
An aspect of the present invention relates to a rotary striking tool which is driven and rotated by a motor to thereby fasten a fastening subject such as a screw or a bolt by using an intermittent striking force.
2. Description of the Related Art
A rotary striking tool (driving tool) for fastening a screw or a bolt etc. by applying a rotation force or a rotational-direction striking force is known. JP-2005-305578-A discloses an impact driver as the kinds of the rotary striking tool. In the impact driver disclosed in JP-2005-305578-A, a hummer part rotates while being axially-movable by using a spring or a cam mechanism, and a hammer strikes an anvil once or twice with respect to a single rotation of the anvil. JP-H06-091552-A discloses an oil pulse tool using an oil pulse unit as the striking mechanism.
The oil pulse tool has a feature that the level of the operation sound is low since metal parts never contact to each other. In the oil pulse tool, a motor is used as a power source for driving an oil pulse unit, and the rotation shaft of the motor is directly coupled to the oil pulse unit. When a trigger switch for operating the oil pulse tool is pulled, a driving electric power is supplied to the motor. The rotation speed of the motor is controlled by changing the driving force of the motor in response to the pulling amount of the trigger switch. When the oil pulse unit generates a pulse torque, a strong striking torque is transmitted to a tip tool, whereby a torque sensor detects the peak torque of the output shaft at every striking operation. An angular sensor is provided at the output shaft to detect the rotation angle of the output shaft, whereby the peak torque value is controlled to approach a target torque value in accordance with a difference between the previously-set target curve of the peak torque values from the fastening start timing to the fastening completion timing and the measured peak torque value.
In the oil pulse unit of JP-H06-091552-A, high-pressure air is used as the power source. On the other hand, in recent years, a rotary striking tool using an electric motor is used. According to the rotary striking tool using the electric motor, the peak torque value is detected at every striking operation. For example, a target torque value for the next striking operation is set in accordance with the detected peak torque value at the previous striking operation, and the motor is controlled to perform the striking operation with the target torque value. The motor is stopped when the peak torque value at the striking operation exceeds a reference value for determining the completion of the fastening operation. In the control of the fastening operation, it is important to accurately detect the peak torque value at the striking operation by using the torque sensor. It is important to accurately discriminate the main striking pulse for controlling control the motor, due to the configuration of the oil pulse unit, not only the peak torque (hereinafter referred to as “main striking pulse”); due to the main striking operation but also a peak torque (hereinafter referred to as “half pulse”); and due to a pseudo striking operation that appears at the angular position different by about 180 degrees from the main striking position.